I think.... This is going to be hilarious.
Your Tags started me laughing and it became glorious from there.
That said....
Why restrict yourself? Sure, Necron Tech is likely the biggest shiny around and most suitable for you in terms of compatability. The Gaus weaponry is kinda like your ability to disassemble things with a beam of doom.....
But lets face it, some of the other races have some AMAZING tech you can use too....
Lets look at this faction by faction.
Necrons: Sure, the Pillars are nice, but the Gaus Weaponry, Reactionless space travel and FTL, Material Science, Anti-Grav, Grav Manipulation, Teleportation, micromachines, Phase Weaponry, Tachyon Manipulation, Molecular Disassembly, Lepton Manipulation, Particle Beams, Plasma Tech, Cross-Dimensional Teleportation, Time Manipulation, Mind Control and Quantum locking are all fantastic too. If you can take a Tomb world and study it all, I doubt you will run out of Technology to use.
Eldar: True, most of the Wraithbone tech may be a bit out of your reach, due to, you know, needing to be a Psyker to make, use, control or do anything worthwhile with it.....But they also have Force Weaponry you can adapt, Power Weapons, some really shiny Plasma tech, they have some Dimensional technology, teleportation, Webway, monofilament, Micro-rockets that are all shades of shiny and best of all, their Shuriken tech is begging to be used by you. Oh yeah, Grav Manipulation and Light/Illusion tech too.
Orks: They might not have any real tech you can't get better elsewhere, but you forget their primary use. As a test bed for any and all weapons and equipment you develop. The survivors will thank you for it too.
Humans: Ok, lets start off by pointing out, most of their stuff, you can get better elsewhere. That said, their Laser Tech is awesome for it's ability to scale up and down. Shields, Gellar Fields, Personal Shields, (Rosarius), Void Shields, Adamantine, Ceramite, teleportation, time manipulation (If you can find it, it does exist though), some cyber-ware, Bolter-tech, gravity manipulation.
The Tau: Ok, they have some decent cloaking tech, some more gravity manipulation, railguns, An FTL that won't kill you until you get the Necron FTL, Ion weapons, smart-missiles and a few other things. Aside from that, similar to the Orks. Just tell them it's for the Greater Good.
Dark Eldar: People tend to forget that these, as twisted and fucked up as they are, are second only to the Necrons as the most technologically advanced race. Grav Manipulation, Dark Matter tech, Nanotech, mind control tech, disintegrators, Really really good Stealth Tech, really nasty Lasers and most importantly of all, Black Hole manipulation, creation and control.
Just don't forget, that once you have smashed your way through all the races tech, in theory, you can have units enter the Warp and kill everything there too.